Centrifuge equipment is used to separate biological and chemical samples into their constituent components based upon differences in their masses (or molecular weights). This is accomplished by placing the samples in appropriate containers and exposing them to centrifugal force. A centrifuge rotor is a relatively massive component of a centrifugal device which is adapted to expose the samples contained therein to such forces. Typically, a rotor is spun up to very high rotational speeds in order to achieve the centrifugal forces needed for a particular separation experiment. It is therefore critical that the rotor is securely coupled to the drive shaft which transmits a drive torque to the rotor.
The availability of a variety of rotors increases the utility of the centrifugal equipment in biological and chemical separations. For a selected separation process, a rotor is chosen according to the sample of interest and the physical characteristics of the rotor. The centrifuge must be adapted to interchangeably mount any of a variety of rotors onto a drive shaft. Conventionally, a centrifuge rotor is connected to the drive system by a drive hub. The hub is fixed to a drive shaft of the drive system and is releasably coupled to the rotor. Numerous approaches have been developed for easy coupling and decoupling of a rotor to and from its drive shaft.
For example, U.S. Pat. No. 4,753,630 discloses a rotor locking mechanism which lockably engages the rotor at a protrusion on the underside thereof. The drive spindle is received in the locking mechanism, thereby imparting a driving force to the rotor. The material constituting the locking mechanism and the design itself are such that the mechanism will fail when a rotational speed which could damage the rotor is attained. Failure of the mechanism disengages the drive spindle from the rotor in that situation, thus saving the rotor from injury.
U.S. Pat. No. 4,890,947 describes a rotor having a mounting adapter. The mounting adapter includes an internal chamber into which is received a connecting member. The rotor/adapter is coupled to the drive spindle by screwing down the connecting member, causing it to press down upon the lower surface of the internal chamber thus securing the adapter to the drive spindle. Conversely, the rotor/adapter is decoupled from the drive shaft by unscrewing the connecting member, causing it to push up against an upper surface of the interior chamber thus lifting the adapter from the drive spindle.
U.S. Pat. No. 5,362,293 discloses a rotor having a clutch mechanism which fits about the circumference of the drive spindle. The clutch comprises two sets of pivotal elements disposed about and in frictional contact with the circumference of the spindle. When the spindle is spun in a clockwise direction, the frictional contact causes one set of pivotal elements to be wedged against the spindle. This wedging action increases the frictional engagement between the clutch and spindle, thereby driving the rotor via the clutch.
U.S. Pat. No. 5,658,231 describes a centrifugal chuck having finger-like members disposed about its periphery for gripping the outer circumference at the base of a rotor. The finger-like members are pivotally mounted to pivot in a radial direction either toward or away from the rotor. The center of mass of each finger-like member is positioned below the pivot point so that the presence of a centrifugal force urges the fingers toward the rotor, thus securing the rotor in place.
These prior art approaches involve mechanical designs which are costly to produce and which are subject to failure over time. In other designs, the rotor is provided with an axial bore along its entire length. A hub fixed to the drive shaft and having outwardly projecting prongs mate with corresponding recesses in the axial bore of the rotor, thus locking the rotor in a fixed position relative to the drive shaft. A tie-down stem is inserted through the bore from the top of the rotor and is coupled to the drive shaft, thus securing the rotor in place. However, the formation of an axial bore greatly weakens the structural integrity of the rotor, introducing stresses at the rotor/bore interface which limit the rotor's working life or limit the maximum speed at which the rotor can operate.
A need therefore exists for providing a mechanically simple locking device which can provide a secure attachment of a centrifuge rotor to its drive system with minimal impact on the structural integrity of the rotor. It is desirable that such a locking device have minimal impact on the longevity of the rotor and on its operating speed.